What for? A metric like that is useless when dealing with an FPGA. The area of a Xilinx FPGA die is the same for all devices with the same part number. If you want the area of the user logic portion of the die, that is basically useless as a metric to tell you anything about the utilization of the device. That is why the utilization reports have things like the number of slices/LUTs/BRAMs/DSP/etc elements are used.